1. Field of the Invention
This invention relates to an optical pulse multiplex unit producing an optical pulse train.
2. Description of Related Art
A conventional optical pulse generator is set forth, for example, in US 2003/0012236A1. The function and structure of the optical pulse generator will be briefly explained with reference to FIG. 15. The optical pulse generator shown in FIG. 15 is constructed with a laser source 51, a delay structure 52, a condenser lens 53, and a wave-guide 54. The delay structure 52, as shown in FIG. 16, has a step-like contour. This can be thought of as an arrangement of a plurality of plane-parallel plates that are equal in refractive index but different in thickness. The plane-parallel plates are arranged at equal intervals in a direction perpendicular to the optical axis. The difference between thicknesses of adjacent plane-parallel plates, measured along the optical axis, is kept constant. When an optical pulse emitted from the laser source 51 is rendered incident as a plane wave on the delay structure 52, a change is caused to an optical path length in accordance with the thickness of the plane-parallel plate through which the optical pulse passes. Specifically, as indicated by numerals 551, 552, . . . , 55n in FIG. 16, a wavefront is stepwise modulated. Such light is collected by the condenser lens 53, and thereby an optical pulse train is transmitted to the wave-guide 54.